1. Field of the Invention
This invention relates to a positive type photosensitive resin composition which has a high sensitivity, can give a pattern with a high yield of residual film thickness and is excellent in adhesion to an encapsulating resin and a substrate, and to a semiconductor device provided with a film which is formed from the above positive type photosensitive resin composition and which relaxes the impact due to the working of molding a resin during encapsulating and also relaxes the stress caused in various thermal histories after the molding.
2. Description of Related Art
Polyimide resins having excellent heat resistance, excellent electrical characteristics and excellent mechanical characteristics have heretofore been used for a surface-protecting film of a semiconductor element and an interlaminar insulation film of a semiconductor element. Recently, however, a remarkable enhancement of heat cycle resistance, thermal shock resistance and the like have been required because of the high integration and largening of a semiconductor element, the thinning and miniaturization of an encapsulating resin package, the transfer to surface mounting by a solder reflow and the like, and hence, a polyimide resin having higher performances has become required.
On the other hand, the spotlight of attention is now being focused on a technique of imparting photosensitivity to a polyimide resin itself, and the polyimide resin to which photosensitivity has been imparted by the technique include, for example, those represented by the following formula (16) and the like: ##STR3##
When these polyimide resins are used, a part of the pattern-forming step can be simplified and they have an effect of shortening the step. However, in the development step, a solvent such as N-methyl-2-pyrrolidone or the like becomes necessary, so that the use of the above polyimides has a problem in respects of safety and handling. Recently, therefore, there has been developed a positive type photosensitive resin which can be subjected to development with an aqueous alkali solution. For example, JP-B-1-46,862 discloses a positive type photosensitive resin composed of a polybenzoxazole resin and a diazoquinone compound or of a polybenzoxazole precursor and a diazoquinone compound. This photosensitive resin has high heat resistance, excellent electrical characteristics and fine processing properties and also has a possibility of use as not only a wafer coating resin but also an interlaminar insulation resin.
In the development mechanism of the above positive type photosensitive resin, the diazoquinone compound in the unexposed portion is insoluble in an aqueous alkali solution and causes, when exposed to light, a chemical reaction to become soluble in an aqueous alkali solution, and the utilization of this difference in solubility between the exposed portion and the unexposed portion makes it possible to prepare a coating film pattern composed of only the unexposed portion.
When such a photosensitive resin is actually used, the sensitivity of the photosensitive resin particularly becomes a problem. When the sensitivity is low, the exposure time per one sheet of wafer becomes long, and the throughput becomes low. Therefore, when, for example, the molecular weight of the polybenzoxazole resin as the base resin is made small for the purpose of enhancing the sensitivity of the photosensitive resin, there are caused such problems that the film loss of the unexposed portion during the development becomes large and the pattern shape becomes bad.
Moreover, the adhesion between the photosensitive resin and the encapsulating resin is bad, and delamination is caused at the interface therebetween, so that there is a problem in practical use. Hence, a photosensitive resin having much better adhesion to the encapsulating resin has become strongly demanded.
Furthermore, in the case of the above positive type photosensitive resin, the removal of the resin in the via hole portion is effected using an alkaline aqueous solution, so that no organic solvent is required unlike other conventional photosensitive polyimide resins and hence the safety of working is further increased.
However, the above photosensitive polybenzoxazole precursor is inferior in adhesion to a substrate, particularly a silicon wafer, and has such a serious problem that the resin is peeled from the substrate by a treatment at a high temperature at a high humidity after curing. This problem cannot be completely solved by adding to the precursor a silane coupling agent or the like which is put on market for improving adhesion, and at present, the use thereof is severely limited.